The present invention relates to apparatus for performing total liquid ventilation on patients. More particularly, the invention is related to inspiration and expiration pumping systems for liquid ventilators.
Liquid ventilation is a procedure involving temporarily filling pulmonary air passages with an oxygenated liquid medium. It was first demonstrated that mammals submerged in hyperoxygenated saline could breathe liquid and successfully resume gas breathing in 1962. However, this approach to liquid ventilation (LV) was eventually abandoned, due to the practical difficulties of dissolving sufficient quantities of O.sub.2 in saline (even at hyperbaric pressures), and because saline rinses away much of the surfactant lining the lung alveoli. These problems were overcome in 1966 by Dr. Leland Clark, who was the first to use perfluorocarbon liquids (now oxygenated at atmospheric pressure) to support the respiration of mice, cats, and puppies.
Perfluorocarbon (PFC) liquids are derived from common organic compounds by the replacement of all carbon-bound hydrogen atoms with fluorine atoms. These liquids are clear, colorless, odorless, nonflammable, and essentially insoluble in water. PFC liquids are denser than water and soft tissue, and have low surface tension and, for the most part, low viscosity. Perfluorocarbon liquids are unique in their high affinity for gases, dissolving more than 20 times as much O.sub.2 and over 3 times as much CO.sub.2 as water. Like other highly inert fluorocarbon materials, perfluorocarbon liquids are extremely nontoxic and biocompatible.
In particular, perfluorocarbon liquid ventilation is a promising treatment of respiratory distress syndromes involving surfactant deficiency or dysfunction. Elevated alveolar surface tension plays a central role in the pathophysiology of the Respiratory Distress Syndrome (RDS) of prematurity and is thought to contribute to lung dysfunction in the Adult Respiratory Distress Syndrome. Perfluorocarbon liquid ventilation is effective in surfactant-deficient premature animals because it eliminates air/fluid interfaces in the lung and thereby greatly reduces pulmonary surface tension. Liquid ventilation can be accomplished at acceptable alveolar pressures without impairing cardiac output and provides excellent gas exchange even in very premature animals.
In liquid ventilation, perfluorocarbon liquid is extracorporeally oxygenated and purged of carbon dioxide, and tidal breaths of the liquid are mechanically cycled into and out of the lungs. Many investigators have utilized gravity-induced ventilation whereby reservoirs above and below the level of the patient's lungs induce inspiration and expiration respectively.
As an alternative to such gravity based systems, pumped liquid ventilators have been used. However, these systems have generally been complex in nature, having two or more peristaltic pumps and fluorocarbon reservoirs in order to provide sufficient user control over inspiration, expiration, tube priming, and other functions performed by the ventilation system.